This purchase is for a pair of front axle / fork sliders that help protect your bike in case of a low-side. It allows the fork to slide on the plastic puck instead of the fork itself. The installation is a simple bolt on with the bar going through the axle and one plastic puck on each side. The slider puck is made of UHMW-PE (ultra high molecular weight polyethylene), a tough plastic with good strength, wear resistance and dimensional stability.It is used in many industrial ball bearing and friction reducing applications. It is softer than Delrin as the result It can absorbs more impact and is less susceptible to cracking. They can be inexpensively replaced in case of a low-side. The bolt is made of 304 stainless steel. Rest assured that you are getting the best material commercially available.